The present invention relates to aircraft performance and control and, more particularly, relates to variable leading edge flaps for use on hypersonic waverider-type aircraft.
As is known in the art, an aircraft traveling at Mach 1 or higher produces a shock wave in air. If the aircraft is tailored correctly, it can be designed to ride this shock wave to produce greater lift, less drag, greater range, and overall improved performance. Such aircraft are commonly referred to as waveriders. Waveriders are particularly useful at high Mach numbers when shock losses (wave drag) become increasingly large. Waveriders reduce shock losses by reducing the shock angle necessary to generate the required lift, which improves the lift-to-drag (UD) ratio of the aircraft and, thus, improves its overall performance. As best seen in FIG. 1, a comparison of conventional aircraft and waveriders is illustrated showing the UD ratio of waverider and conventional aircraft for speeds above about Mach 2. In this graph, one can see that although UD ratios above about 7 are difficult to achieve at speeds higher than Mach 5 for a conventional aircraft, a waverider is capable of 30-50% higher UD ratios than conventional aircraft operating at the same speed. Furthermore, as can be seen from FIG. 1, this improved UD ratio and thus overall performance is most pronounced at hypersonic speeds, which typically begins at about Mach 5.
According to supersonic flow theory, as supersonic flow passes over a wedge body, a shock wave is formed at the apex (point) of the wedge. This shock wave produces compression lift. Compression lift is that lift produced due to the increase in surface pressure exerted on the underside of a supersonic vehicle due to the pressure rise across a shock wave. Maximizing compression lift is the principle benefit of the waverider concept.
In general, hypersonic aircraft suffer from low UD ratios. However, in order to overcome this problem, waveriders are designed to maintain an attached shock along their leading edges. That is, the shock wave is not detached from the leading edge, where detachment would allow high-pressure air that generates lift to spill around the leading edges, reducing lift, thereby requiring an increase in wing angle-of-attack to maintain lift, with an attendant increase in shock angle, wave drag, and induced drag. The wings thus are able to maximize the compression lift created by the shock wave, without adding any unnecessary drag; however, as will be described below, conventional waverider wing designs are only optimized for a single Mach speed and angle of attack condition.
Generally, waverider aircraft provide numerous advantages over conventional aircraft when travelling at high Mach speeds, such as, but not limited to, producing only positive lift; maintaining an attached leading edge shock, which minimizes spillage of high-pressure air from the bottom surface of the wing, thereby minimizing lateral flow losses; and minimizing cross flow, which aids in maintaining natural laminar boundary layer flow, which reduces frictional drag and aerodynamic heating.
Unfortunately, conventional waveriders are typically designed for use at a single, specific Mach number and a specific angle of attack. That is, the bow shock wave created by a typical hypersonic wing, including a waverider, detaches from the wing leading edge when the combination of Mach number and flow incidence angle resolved in a plane normal to the leading edge is outside the range that would yield an attached shock solution on a two-dimensional wedge, as seen in FIG. 2. Under detached shock conditions, flow can spill around the wing leading edge, thereby reducing lower surface pressure and, thus, lift. Accordingly, the particular usefulness of waveriders may be limited to a very small operational envelopexe2x80x94a small range of Mach number and angle of attack. This small operational envelope inhibits high-performance operation outside of the predetermined set of narrow parameters and, thus, limits the versatility and performance of conventional waveriders.
Therefore, there exists a need in the relevant art to provide a hypersonic aircraft that is capable of operating as a waverider within a broader operational envelope. Furthermore, there exists a need in the relevant art to provide a hypersonic waverider aircraft capable of changing its structural configuration to accommodate varying Mach numbers and angles of incidence. Still further, there is a need in the relevant art to provide a hypersonic waverider aircraft capable of overcoming the disadvantages of the prior art.
According to the teachings of the present invention, a hypersonic aircraft having an advantageous construction. The hypersonic aircraft produces a shock wave during hypersonic flight. The shape of the shock wave changes depending upon dynamic variations attributed to changes in Mach speed and flight attitude. The aircraft includes a body, a pair of wings coupled to the body having leading edges (or a blended wing-body), and a deflectable flap system operably coupled to the leading edge of each of the pair of wings. The flap system is positionable in a plurality of positions relative to the pair of wings so as to achieve a generally optimal position capable of maintaining attachment of the shock wave along the leading edge of the flap system at hypersonic speeds. A controller is further operably coupled to the deflectable flap systems for determining the optimal position and outputting a signal that drives the flap system.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.